Spring frosts and subsequent crop losses threaten the economic sustainability of fruit crop producers all over the world. This study used a controlled-freezing technique to impose a post-budburst freezing stress to grapevine shoots forced from one-node cuttings [‘Albariño’, ‘Cabernet Franc’, ‘Cabernet Sauvignon’, and ‘Pinot Grigio’ (Vitis vinifera)] and whole plants [‘Noiret’ (Vitis hybrid)]. Our goal was to investigate the incidence of freeze injury among cultivars, stage of phenological development, and a potassium salt-based fertilizer (KDL) with potential cryoprotectant activity. Among the V. vinifera cultivars, the incidence of mortality of shoots exposed to −3.5 °C was highest for ‘Albariño’ (71%) and lowest for ‘Cabernet Sauvignon’ (51%). Cuttings sprayed with KDL 24 hours before cold temperature exposure exhibited 16% lower shoot mortality and lower osmotic potential (Ψs) (−0.92 MPa) than the unsprayed cuttings (−0.77 MPa). However, application of KDL did not impact shoot mortality for whole ‘Noiret’ vines. Mortality for ‘Noiret’ shoots greatly increased with the advancement of phenological development, ranging from 10% in wooly buds to 78% in shoots ≈10-cm long. The practical significance of KDL remains questionable; cultivar selection still appears to be a more reliable method for avoiding spring frost, by planting late bursting cultivars in more frost-prone areas.
Open-pollinated seeds from grapevines in Parlier and Davis (in California) and Geneva (in New York) were collected in 2016, 2017, and 2018. Seeds were subjected to a series of cold stratification treatments of varying lengths and germinated in incubators to compare germination rates. Two V. vinifera cultivars (Chardonnay and Cabernet Sauvignon) and three other cultivars (V. labrusca hybrids) with a similar genetic background were compared across three locations to test for maternal environmental effects on germination rates under different cold stratification durations. Two interspecific hybrids (‘Salamander’ and ‘Sovereign Rose’) and three genotypes each from two species, V. riparia and V. cinerea, were evaluated to compare germination rate variability at different cold stratification durations among and within species and hybrids. Large variability in germination rates was evident among and within grape species, with some accessions requiring little to no cold stratification, and others requiring 10 to 12 weeks. These differences could be useful for breeding grapevines with high or low dormancy requirements. The maternal plant environment impacted the seed weight and total seed germination across years and locations.